The present invention relates to an ink jet print head comprising an ink reservoir connected to at least one print element having an ink outlet, a piezoelectric transducer which is actuable by a pulse generated selectively by a control circuit for causing the emission of a drop of ink through the outlet, and a circuit for detecting the pressure of the ink in the element during the printing operation.
For an ink jet printer to operate correctly, especially one in which emission is controlled by a pressure pulse generated for example by a piezoelectric transducer, the print element must be completely full of ink. Arrangements are known which can be actuated to purge the print elements in a purge station at the beginning of the print operation. Those arrangements are actuated as a precaution independently of the operation of filling the print element, with the result that they often cause an accumulation of ink which has been purged in the purge station.
Devices are also known which can be actuated to remove any bubbles of air from the print element. In U.S. Pat. No. 4,466,005, there is described an arrangement for removing bubbles of air from a print element, which is controlled automatically by an electrical signal generated by a bubble detection circuit. The arrangement comprises a circuit which is operable to generate trains of pulses at various frequencies and voltages, in such a way as to eliminate various types of bubbles. That arrangement is complicated but is not capable of purging the print element when the element is completely empty.